ZXMUX Tester Shield

The ZXMUX chip (ZX8401 / PCF1306P / 40058) is a custom multiplexer chip designed for and used in the ZX Spectrum 128, +2, 48 Issue 5 and 6A.

As this is a custom chip, modern chip testers like the TL866 is unable to test them. If you are troubleshooting a Spectrum and you don’t have a known good working device to test the multiplexer in, this makes it difficult to troubleshoot.

I built an shield for the Arduino Mega 2560 which tests the multiplexer as it’s a fairly simple design that uses logic NAND/OR gates and digital multiplexers. I use this to also test the ZXMUX replacement chips that I sell on my store.

To use this shield you will need to have a Arduino Mega 2560 (Not included in sale) and have some knowledge using avrdude (to upload the hex firmware to the Arduino) and Arduino IDE to view the serial output results from the test.

For more instruction on using this shield see my github page.